1. Field of the Invention
The invention generally relates to a photoelectric apparatus and a control method, and more particularly, to a light emitting apparatus and the control method.
2. Description of Related Art
The light emitting principle of the semiconductor device used for emitting light uses the special character of the semiconductor device and is different from the light emitting principle of the general fluorescent lamp and the incandescent lamp. The semiconductor devices used for emitting light have many kinds. The light emitting diode has the advantages of high illumination output, small volume, low driving voltage, and mercury free, so the light emitting diode is widely used in illumination and display apparatus area.
To make the light emitting diode be used in all kinds of products, the institution of rule becomes very important. Generally speaking, a rated driving power of the light emitting diode is an important parameter to determine the light emitting power, and when the light emitting diode operates, the light emitting diode is driven by the rated driving power. However, the rated driving power is not the only parameter affecting the light emitting power of the light emitting diode. When a junction temperature of the light emitting diode rises, the light emitting power of the light emitting diode reduces. Seriously, the light emitting power of the light emitting diode with high rated driving power and high junction temperature may be less than the light emitting power of the light emitting diode with low rated driving power and low junction temperature.
For example, as shown in FIG. 1, the X-coordinate stands for the operating time of the light emitting diode, the Y-coordinates in the left and right sides are respectively stand for the junction temperature and the light emitting power of the light emitting diode, curves T16 and L16 respectively stand for the characteristic curve of the light emitting diode when the rated driving power is 1.6 watt, and curves T10 and L10 respectively stand for the characteristic curve of the light emitting diode when the rated driving power is 1 watt. The curves T16 and T10 respectively stand for the relation between the junction temperature and the time of the light emitting diode when the rated driving power is respectively 1.6 watt and 1 watt, and the curves L16 and L10 respectively stand for the relation between the light emitting power and the time of the light emitting diode when the rated driving power is respectively 1.6 watt and 1 watt.
From above, from the curves L16 and L10, when the two light emitting diodes emit light, the light emitting power (about 301 mW) of the light emitting diode with the rated driving power 1.6 watt is more than the light emitting power (about 244 mW) of the light emitting diode with the rated driving power 1 watt. In addition, from the curves T16 and T10, although the junction temperature of the light emitting diode with the rated driving power 1.6 watt is more than the junction temperature of the light emitting diode with the rated driving power 1 watt, and the temperatures of the two light emitting diodes have less differences.
However, after the above-mentioned two light emitting diodes emit the light continuously for 6000 seconds (about 1.6 hours), the light emitting power of the light emitting diode with the rated driving power 1.6 watt has reduced to about 174 mW, and is less than the light emitting power (about 176 mW) of the light emitting diode with the rated driving power 1 watt. The junction temperature of the light emitting diode with the rated driving power 1.6 watt is higher than the junction temperature of the light emitting diode with the rated driving power 1 watt.
From the above, during the time of continuously emitting the light for 6000 seconds, the light emitting diode with rated driving power 1.6 watt has bigger temperature programming than the light emitting diode with rated driving power 1 watt, so the light emitting diode with rated driving power 1.6 watt has more power consumption and the light emitting power is reduced as a result.